Method and means for hydrocarbon synthesis



Feb. 1, 1949.

E. A. JOHNSON ET AL METHOD AND MEANS FOR HYDROCARBON SYNTHESIS FiledJuly 30, 1946 h'x/orocarbon Feed 7 CH4 Reformer Z 7 l5 l5 Iron Cobo/f C2 l f a a ys 22\ Cafa/ysf -26 Recovery Recovery Sysfem Sysfem P3 P0Producf Producf Separafion A? lnvenfors:

Evereff A Johnson Sam 8. Becker Affo r'n ey mama Feb. v1, 1949 METHODAND MEANS FOR HYDROCARBON SYNTHESIS Everett A. Johnson, Park Ridge, andSam B. Becker, Chicago, Ill., assignors to Standard Oil Company,Chicago, 111., a corporation of Indiana Application July 30, 1946,Serial No. 687,064

This invention relates to the synthesis of hydrocarbons having more thanone carbon atom in the molecule and it pertains more particularly to animproved method and meansfor producing normally liquid hydrocarbons byreacting hydrogen and carbon monoxide over catalysts under optimumconditions. More specifically it relates to hydrocarbon synthesis withmethane as the raw material.

When methane from natural gas is reformed by direct combustion withoxygen, a certain amount of excess heat is available especially if thefeed gases are preheated to temperatures of about 1000" F. or higher andthe reforming car- 'ried out in the presence of a catalyst. Carbondioxide can be incorporated in the feed gas in quantities suflicient toabsorb excess heat by reacting it endothermically with a portion of thenatural gas. The incorporation of carbon dioxide in the feed gas notonly simplifies the design of the reformer by making the operationthermally balanced, but also increases the overall carbon efficiency ofthe process. Consequently from the standpoint of thermal and carbonefficiency it is desirable to feed to the'reforming operation a gascomprising methane, oxygen and carbon dioxide.

However, when methane, oxygen and carbon dioxide in the properproportions are reformed catalytically at relatively high temperatures,the make gas produced is not ideally suited for the synthesis reactionusing either cobalt catalyst, for which it is deficient in hydrogen,orfor synthesis using iron catalyst, for which it is dea gas compositionmore nearly ideal for the c0-v balt' catalyst operation. Likewise, atleasta part of the unconverted'gas from the cobaltcatalyst synthesis canbe blended with a second portion of the make gas from the reformingvunitfg'lving a gas composition very nearly ideal for the iron catalystoperation.

When make gas having hydrogen and carbon- 2 Claims. (Cl. 260-44915) aconsiderable proportion of the reaction product is olefinic but theextent of conversion is relatively low.

The formation'of hydrocarbons by contacting make gas with a cobalt typecatalyst requires a make gas mixture which contains hydrogen and carbonmonoxide in the ratio of about 2 to 1 in order to obtain the desiredproducts. However, even under optimum conditions, a substantialproportion of the carbon monoxide remains unconverted to recoverablehydrocarbon rich in oleflns. It is, therefore, another object of thisinvention to provide a process for increasing the carbon monoxideconversion and to increase the yield of hydrocarbons from a given makegas mixture. I

In the synthesis of hydrocarbons from make gas by means of an ironcatalyst the reaction takes place largely in accordance with thefollowing equationz.

In this reaction one-half the volume of hydrogen based upoh carbonmonoxide is consumed so that the residual make gas has a higherproportion of hydrogen than the fresh feed. With the use of higherhydrogen to carbon monoxide ratios the following average reactionoccurs:

In the conversion of make gas over a cobalt type catalyst the reactionis principally in accordance with the following equation:

Therefore, in this reaction about twice the volume of hydrogen pervolume of carbon monoxide is consumed.

The term make gas as used herein refers to gases containing carbonmonoxide and hydrogen. The normal make gas prepared by the reforming ofmethane by conventional methods contains carbon monoxide and hydrogen inthe ratio of between about 1 to 1 and 3 or 4 to 1. The hydrogen ratio inthe gas from a thermally balanced reforming operation in which the feed[gases comprising CH4, CO: and O2 is usually within the range of 7 to 4'and 5 to 4. In general the higher the thermal emcienc'y and the higherlower the hydrogen to carbon monoxide ratio.

However,' such a make gas ordinarily is not monoxide in the ratio ofabout 1:1 is contacted V with an iron type catalyst under suitableoperating conditions of temperature and pressure,

suitable] for the synthesis of optimum quanti- 1 ties ofliquidhydrocarbonsover either iron or cobalt catalysts, and it has heretoforebeen nec- 3 essary to alter the proportions of hydrogen to carbonmonoxide in the make gas depending upon whether an iron or cobalt typecatalyst is to be used. Such treatment of the make gas obviouslycomplicates the system and increases the cost of the product.

Therefore, a further object of this invention is to provide a systemadapted to produce increased quantities of useful hydrocarbons andchemicals from a given make gas. Another object is to provide animproved system for the optimum utilization of hydrogen and carbonmonoxide produced by the reformingof methane. Another object is toprovide an improved system for the optimum utilization of hydrogen andcarbon monoxide produced by the reforming of methane. Another object isto produce a uniquely integrated system wherein substantially completecleanup of carbon monoxide is obtained. A more specific object of ourinvention is to provide a multiple catalyst system wherein a singlesupply of make gas is utilized to produce optimum quantities of thedesired product. These and other objects of the invention. will becomeapparent to those skilled in the art as the description of our inventionproceeds.

Briefly, our inventioncontemplates dividing a stream :of make gas havinga hydrogen to carbon monoxide ratio which is optimum neither for irontype catalyst nor cobalt type catalyst and supplying substantially equalparts of the make gas stream to separate parallel reaction zones. In onezone is provided a cobalt type catalyst and in the other is an iron typecatalyst. In the cobalt synthesis zone a substantial proportion ofcarbon monoxide is unconverted and this carbon monoxide is used tosupplement the make gas fed to the iron catalyst synthesis. On the otherhand, substantially complete cleanup of carbon monoxide is obtained inthe iron catalyst synthesis and there is an increased proportion ofhydrogen in the unconverted gases. Another product of the iron catalystsynthesis is carbon dioxide which is separated and can be recycled tothe methane reformer which produces the initial make gas. Theunconverted hydrogen. recovered from the iron catalyst synthesis can beused to supplement the make gas supplied to the cobalt catalystsynthesis bringing the feed within the optimum proportions of hydrogento carbon monoxide for the cobalt synthesis. Thus, a system is providedfor maximum hydrogen consumption over cobalt catalyst, maximum carbonmonoxide cleanup in iron catalyst synthesis and maximum utilization ofcarbon dioxide in reforming additional quantities of methane.

An essential feature of the process is that the make gas which is notparticularly suitable for either cobalt synthesis or iron synthesis isrendered useful in an exceptionally convenient and economical manner.

The hydrogen-carbon monoxide mixture can be suitably obtained fromnatural gas (which may consist chiefly of methane) as the raw material.However, my invention is not limited to the source of the carbonmonoxide-hydrogen mixture and may be obtained for example from coal,shale, tars, or other carbonaceous materials.

The basic equations for the gas reforming operation using methane may besomewhat as follows:

(a) CH4+CO2= 2CO+ H2 CH4+.50:=CO+2H2 The recycle gas of course containsethane and 4 ethylene as well as methane andunreacted make gas but thereaction of these hydrocarbons is similar to that indicated above. Theproportions of carbon dioxide and steam and/or oxygen containing gascan. in any case be so adjusted to give the desired make gas.

The natural gas can be first freed :of hydrogen sulfide or organicsulfur compounds, for example by scrubbing with a suitable solvent,followed if necessary by scrubbing with a strong caustic solution.Likewise, the gases may be desulfuri'zed by contacting with luxmasse.The desulfurized gas is then mixed with such proportions of carbondioxide and oxygen and/0r steam .to give a gas mixture having an atomichydrogen: carbonzoxygenratio of about 411:1. The feed can be preheatedto above about 900 F. or an excess of oxygen can be supplied to thereformer as described below. This mixture is then contacted with areforming catalyst preferably with an VIIIth group metal which may besupported on clay, kieseiguhr, silica gel, alumina, etc. Such a catalystfor instance may be a mixture of oxides of nickel, iron and megnesiumwith the proportions l:1: .5, respectively. The nickel or VIIIth groupmetal catalyst may be promoted by oxides of aluminum, magnesium,calcium, cerium, chromium, molybdenum, vanadium, etc.

The space velocity through the reforming catalyst should be sufficientto give a contact time of between about 2 and 60 seconds, preferablybetween about 10 and seconds. The temperature of this operation ispreferably between about 1400 and about 1800 F. and the pressure may beabout atmospheric, to 300 pounds per square inch or higher. If thenatural gas is reformed without a catalyst, temperatures of above about2000 F. are used. This reforming operation converts the methane-carbondioxide-steam or :oxygen mixture into a gas consisting chiefly of hydrogen and carbon monoxide in the proportions of about 5:3.

Carrying out the process in a practical operation is illustrated by thefollowing description taken with the drawings wherein the process isdiagrammatically illustrated. The hydrocarbon charge comprising aboutmillion cubic feet per day is supplied through line In to the reformerll, together with carbon dioxide introduced through line I! and anoxidizing gas which may be oxygen or steam, supplied to the reformer IIby line l3. may be substantially as follows:

Million cubic feet per day Methane 50 Carbon dioxide 10 Oxygen erablyabout 250 pounds per square inch and at a temperature of between about1,400 and l,800 F., for example, 1,500 to 1,550 F. A space velocity ismaintained so as to give a contact time of about 2 to seconds, forexample about 10 The daily charge to the reformer ii a,sso,sos

to 30 seconds. This reforming is thermally bal anced if feeds arepreheated sumciently. for example to a temperature of about 1000 to1200' I. and if outlet temperature is between 1400 and l600.l". If nocatalyst is used. the oxygen or degree of preheating should beincreased.

As stated above, the catalyst, when used for this reforming step, may beone or more VIIlth group metals such as nickel, iron, or a mixture ofnickel and iron oxide. Such a catalyst may be promoted with the namedmaterials and can be on a suitable flnely divided supp rt. However. noinvention is claimed in the catalyst per ac and since such catalysts arewell-known in the art. a further detailed description thereof isnot-necessary.

make gas system but is applicable to any system producing a make gaswherein the ratio of H: to CO lies within the range of from :4 to 7:4.

The hot make gas withdrawn from the reformer l i can be cooled byconventional means not illustrated. The make gas. comprising about 160million cubic feet per day or about 6.6 million cubic feet per hour. andabout 110,000 cubic feet per minute, is available in line ll. This makegas is split and separate portions passed by lines I! and it to the ironcatalyst synthesis reactor H and the cobalt catalyst synthesis reactorII. respectively. In general, the iron type catalysts operate at highertemperatures and pressures than the cobalt type catalyst.

An active iron type catalyst can be prepared by I a number of methodswell known in the art and can for example be of the precipitated typesupported on super-filtrol or'other finely divided inert carriers.Alternatively, an iron catalyst of the type employed in ammoniasynthesis can be used, such catalyst ordinarily being prepared byoxidizing iron in a stream of oxylen, fusing the resultant mass andcrushing the fused oxide.

thorium, titanium. uranium. sinchzirconium. and the like. The cobaltsupport is preferably an acid-treated bentonite or clay. such as SuperFiltrol or other material which is substantially free of any catalystpoison. Other supports include materials such as kaolin. alumina.silica. magnesia. and the like. The catalyst-to-carrier weight ratio canbe varied between about 0.1:1 and about 5.0:1. The catalyst may bereduced before use, preferably with hydrogen or hydrogenrich as at atemperature of between about 350- 500' 1''. Likewise, the reduction canbe eflected within the reactor proper on contact with the synthesis gas.which is a reducing medium.

Instead of the cobalt catalyst. we may employ a catalyst of the nickelor ruthenium type. The above catalysts are all known in the art andinasmuch as no invention is claimed in their composition or method ofpreparation. a further description thereof is not believed necessary.

The synthesis reactors i1 and may contain either fixed bed or fluidizeddense phase catalysts and the two parallel reactors need not be of thesame type. Thus. for example, the cobalt reactor may contain a fixed bedof catalyst and the iron reactor. a fluidized dense phase catalyst.

If a fluidized dense phase of catalyst is used. the catalyst ordinarilyis in a finely divided form so that it can be fluidized by gases flowingup- A very eflective and economical catalyst can be produced by roastingiron pyrites and adsorbing KF thereon. The iron catalyst can be reducedbefore use, preferable with'hydrogen at a temperature of between about600 and 1.500 I". If desired. however. the make-up catalyst can besupplied to the reactor as the oxide, the oxide undergoing reductionduring the synthesis operation. Another method of preparing the catalystemploys the decomposition of iron carbonyl to form an iron powder whichmay be 'sintered and ground before activation with hydrogen. Catalystparticles without a support will have a bulk density as high as betweenabout 120-150 pounds per cubic foot, whereas the bulk density of ironcatalyst supported on Super Flltrol or similar carrier may be as low asabout ten pounds per cubic foot. u

The iron type catalyst can be promoted by the addition of between about.5 and about 1.5% M- kali metal compound. There is an optimumtemperature of reduction of an alkali-promoted catalyst which isdependent upon the amount of alkali present. For example, with about 1%alkali. the optimum temperature for reducing the fluidized catalyst isabout 850 1''. In general, the optimum reduction temperature at whichfluidization can be maintained is lower with the higher proportions ofalkalimetal compounds.

A cobalt type of catalyst 'employediin the parallel operation of thisinvention can consist essentially of supported cobalt .metal, eitherwith or without one or more promoters-such as oxides .of aluminum,cerium, magnesium; manganese,

wardly through the bed of the catalyst at low velocities, said catalystbeing maintained as a dense turbulent suspended phase. The catalystparticles can be of the order of 2-200 microns. preferably 20-100microns in particle size. 'With vertical gas velocities of the order ofabout 0.5 to 5.0, preferably between about 1 and 4, for example about 2feet per second, a liquid-like dense phase of catalyst is obtained inwhich the bulk density is between about '30 and about preferably betweenabout 40 and 80%, e. g.. about 50%, of the density oi the settledcatalyst material. The vertical velocity of the gases is in any eventregulated so as to produce a turbulent suspension of catalyst within thereactor.

The make gas in line I! is introduced into the -iron catalyst synthesisreactor I1 together with residual gases in line I! from the cobaltcatalyst synthesis reactor is, these residual gases being relativelyrichin carbon monoxide.

With iron catalyst a temperature of between about 400 and 750 F. andpressures of between about '15 and 400 pounds per square inch can beused. A preferred range is a temperature between about 450 and 650 F.and a pressure of between about and about 325 pounds per square inch.However, when an iron catalyst, promoted with about 10 weight per centof cop- .per is used, substantially lower pressures may be employed. Thespace velocity through the reactor should be between about 1,000 and10,000 or more volumes of gas per hour per volume of space occupied bythe dense catalyst phase within the reactor. If desired. substantialrecycle of diluent CO: can be provided to permit higher hydrogenmarbonmonoxide ratios in the make gas passture predominating in hydrogen andcontaining carbon dioxide is separated via line 22. and liquid productfractions including hydrocarbons and water are withdrawn by line 23 forfurther separation or processing. At least a portion ot'the gases inline 22 can be recycled via line I to the iron catalyst synthesisreactor ll. Such recycle oi COz-rich gas has been found to permitoptimum carbon utilization over iron catalyst. The remainder of thegases in line 22 can be supplied to a carbon dioxide separation systemschematically represented at 24 wherein hydrogen and carbon dioxide areseparated. Buch separation can be accomplished by scrubbing withmonoethanolamine or some other solvent for carbon dioxide. Thehydrogen-rich stream is transferred from the carbon dioxide separationzone 24 by line 25 to the cobalt catalyst reactor II. A. portion of thisstream can be vented from the system via line 28 and this stream can beutilized as fuel for adding heat to the reformer H. The carbon dioxideis stripped from the scrubbing medium within the carbon dioxideseparation system 24 and passed through line l2 to the reformer Ii.Likewise, a portion of the recovered C: can be recycled by lines 21 andii to the iron catalyst reactor H to enhance the conversion of carbonmonoxide to hydrocarbons.

The gases in line 25 include hydrogen and carbon monoxide in the ratioof at least to l and may be substantially free from carbon monoxidebecause of the high conversion of carbon monoxide in the iron synthesiscatalyst reactor II. This hydrogen-rich gas stream is c'ommingled withmake gas supplied by line i6 whereby the hydrogen-carbon monoxide ratioof the net feed to the cobalt catalyst synthesis zone i8 issubstantially increased and this provides maximum hydrogen consumptionover a cobalt catalyst.

The catalyst in the cobalt synthesis reactor I! can be of a precipitatedcobalt or nickel type either in a fluidized or stationary bed. Thesynthesis temperatures can be between about 340 and about 500 F.,preferably below about 425 F., and relatively low pressures of not morethan about 50 pounds per square inch and preferably about atmosphericpressure are employed. The space velocity should be in the generalvicinity of between about 50 and 1500 volumes of gas.

per hour per volume of space occupied by the catalyst. Approximately 60to 70% conversion of carbon monoxide is eilfected in the cobalt catalystsynthesis reactor i8. At this conversion, the optimum quantity ofoleflnic hydrocarbons'is produced and the residual carbon monoxide isconverted in the parallel iron synthesis catalyst reactor H.

The synthesis product from reactor i8 is withdrawn via line 28 andintroduced into a recovery system schematically represented at 29. Thisrecovery system ordinarily can comprise means for cooling the product toeflect a separation between gaseous and liquid products, but any type ofseparation and recovery means may be used. The liquid products,including hydrocarbons and water, together with oxygenated compounds,are illustrated as being withdrawn from the recovery system 29 via linefor further separation and processing. This further separation andprocessing can be effected in the same equipment as that used on thecorresponding fractions recovered in line 22 from the parallel ironsynthesis catalyst reactor l1. However, the cobalt catalyst and ironcatalyst reactors can be operated to produce predominantly eitherolefins or paraflins and the paraflins can be isomerized and thenalkylated with the oleflns. Likewise, it is contemplated that gasolinefractions recovered separately from the iron and cobalt synthesis can beblended to yield a product of increased storage stability. The

blended gasoline fractions can be treated by contacting with bauxite inthe vapor phase at 700' to 750 F. at a space velocity oi i to 10 liquidvolumes of hydrocarbon per volume of catalyst per hour. Thisaccomplishes a conversion oi the oxygen compounds to water andhydrocarbons and simultaneously isomerizes the oleiins to a higheroctane number level.

If desired. at least a portion of the synthesis water withdrawn from theproduct recovery systems can be supplied to the reformer II for reactionwith additional methane and carbon dioxide to produce further quantitiesof make gas. The gaseous products withdrawn from the recovery system-2|via line i0 comprise a substantial proportion of carbon monoxide andthis gas is supplied to the iron catalyst synthesis reactor il therebyincreasing the ratio of carbon monoxide to hydrogen in the make gassupplied by line I! to the reactor I]. As discussed above, substantialconversion of carbon monoxide is eiiected in the iron catalyst synthesisreactor IT.

The flow sheet merely illustrates the parallel process schematically andit should be clearly understood that pumps, compressors, valves, meters,and the like have been omitted for clarity, but their use iscontemplated wherever necessary, as good engineering practice dictates.

From the above detailed description, it will be apparent that we haveattained the objects of our invention and have provided an improvedprocess employing parallel units to effect the optimum conversion ofhydrogen and carbon monoxide to hydrocarbon products having more than Ione carbon atom to the molecule and havin high proportions of olefins.The parallel operation affords economic advantages which cannot beobtained with either catalyst system alone using the make gas normallyproduced by the reforming of methane. Likewise, each catalyst systemsupplements the other and utilizes the residual feed gases to improvethe extent of conversion and the character of products obtainable fromgiven make gas. These and other features of our system cooperate toproduce a novel and useful system not heretofore available.

The specific example described in more or less detail is for the purposeof illustration only and it should be understood that our invention isnot limited thereto since other modifications and advantages will becomeapparent to those skilled in the art in view of the above description.

We claim:

1. In the process of converting a gasmixture containing hydrogen andcarbon monoxide initially in a ratio of at least 5:3, the steps whichinclude contacting one portion of the total gas mixture with an irontype catalyst at a pressure above about 5 atmospheres and a temperatureabove about 400 F., contacting another portion of the total gas mixturewith a cobalt type catalyst in a parallel reaction zone at aboutatmospheric pressure and at a temperature between about 340 and 500 F.,separately withdrawing reaction products from said parallel reactionzones recovering from the reaction products withdrawn from the ironcatalyst synthesis a residual gas mixture including hydrogen and carbondioxide. said residual gas mixture having a higher proportion ofhydrogen to carbon monoxide than said total gas mixture separating fromthe reaction products of the cobalt catalyst synthesis agaseous'fraction relatively richer in carbon monoxide than said totalinitial gas mixture, supplyingat least a portion of the hydrogen-richresidual gas from said iron catalyst synthesis to said cobalt catalystsynthesis, and supplying substantially all of the carbon monoxiderecovered from the cobalt catalyst synthesis to said iron catalystsynthesis.

2. The' process of synthesizing hydrocarbons from hydrogen and carbonmonoxide mixtures produced by converting hydrocarbons with carbondioxide and oxygen in a substantially thermally balanced reaction whichincludes the steps of splitting a stream of hydrogen and carbon monoxidegas mixture into substantially equal portions, reacting one portion ofsaid total gas mixture over a cobalt synthesis catalyst, reactinganother portion of said total gas mixture over an iron synthesiscatalyst, recovering residual gases from each of said synthesis steps,supplying residual gas from the cobalt synthesis catalyst zone to saidiron catalyst synthesis zone, recovering separate streams of carbondioxide and hydrogenrich gas from the residual gases withdrawn from theiron catalyst synthesis step, supplying at least a portion of the saidhydrogen-rich gas to said cobalt catalyst synthesis step and utilizingat least a portion of the said carbon dioxide to convert additionalquantities of hydrocarbons into an initial gas mixture of hydrogen andcarbon monoxide in a ratio of about 5:3, and supplying separate portionsof the total gas mixture to said parallel synthesis zones.

EVERETT A. JOHNSON.

SAM B. BECKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,234,941 Keith, Jr. Mar. 11,1941 2,244,710 Kolbel June 10, 1941 2,248,099 Linckh et al. 'July 8,1941 2,417,164 Huber, Jr. Mar. 11, 1947 FOREIGN PATENTS Number CountryDate 515,037 Great Britain Nov. 24, 1939

